1. Field of the Invention
The present invention relates to a character reading circuit for accessing a character area for storing characters, such as letters or the like, to read character data for displaying a character on a display such as a television screen, and in particular to a character reading circuit capable of partial reading from a character area.
2. Description of the Related Art
A known conventional TV equipment allows display of RGB processed color characters on a TV screen according to predetermined code data, the code data being reproduced from a received signal or generated internally.
For character display, a character ROM and a video RAM are provided to such equipment. A character ROM stores dot patterns (character patterns) of predetermined character fonts, and a video RAM stores character codes for specifying an access address in the character ROM. Addresses of the video RAM correspond to character display positions on a TV screen. Therefore, characters are displayed through reading corresponding character patterns from the character ROM according to character codes stored at the respective locations in the video RAM.
Here, a character area in the character ROM for storing each character, is addressed by a character code stored in the video RAM and has a constant size. Meanwhile, each character may be displayed on a screen in one or more of a variety of sizes, including large and small character sizes. Storing a single small character in a character area with the capacity to store a larger character is an inefficient use of memory space. In light of this, a circuit capable of partial reading from a character area is proposed in Japanese Patent Laid-open publication No. Hei 9-212332. With this circuit, two or more characters can be stored in one character area, and each of the characters stored in one character area can be separately read out therefrom. This allows efficient utilization of ROM capacity.
Also, when a character is displayed in a color overly similar to that of the background, the character can may be recognizable, or may be difficult to recognize. To address this problem, each character may be bordered for clarification. That is, bordering a character in a color different from that of the character creates easily recognizable characters. In addition,xe2x80x9cborderingxe2x80x9d may be called asxe2x80x9cfringexe2x80x9d.
As a bordering algorithm, when a dot to be processed (an object dot) is a background dot and at least one of the dots above, below, to the left, or to the right side of the object dot is a foreground dot (a dot for character displaying), the object dot is bordered. That is, the object dot is set in a bordering color which is different from the color of an associated character. Such bordering processing can be efficiently achieved using a circuit such as is disclosed in Japanese Patent Laid-open No. Hei 10-240222. With the disclosed circuit, data for three rows can be read in parallel, and bordering processing can be performed based on that data.
This circuit, however, has a problem in that inappropriate bordering may be made when data is read through partial reading from a desired character area. That is, for bordering with respect to the head or end line of a partially read section, data on lines above and below the partially read section is also read, similar to bordering with respect to other lines, to be subjected to bordering processing. Therefore, the bordering processing is affected by data for a section (out-part data) adjacent to the partial reading section. As out-part data is not displayed, bordering based on the out-part character data should be avoided.
To prevent undesirable influence of this type, in one possible method, character data is prevented from being written in a line adjacent to the boundary of a partial reading part within one character area. However, maintaining a line of character dots which are never used wastes capacity of the character area.
The present invention aims to provide a character reading circuit capable of partial reading of character data without adversely effecting bordering processing.
According to the present invention, in a character reading circuit capable of reading character font data through partial reading from one character area designated by one character code, modification of data stored in the section to be partially read (in-part data) based on data stored in a section adjacent to the partially read section (out-part data) is prohibited.
Here, when a character area is divided into partial reading sections and bordering processing is applied, when character data not to be read is located adjacent to a section storing data for reading, bordering will be made only within the concerned part. An arrangement of the present invention can prevent unnecessary data modification by prohibiting data modification.
In addition, preferably, in-part data may be read in the place of out-part data for use in modification of the in-part data. With this arrangement, out-part data is not read, and bordering based on out-part character data can be prevented.
In this case, when reading character font data, data on lines above and below a data reading line is read together with data on the data reading line so that data on the data reading line is modified based on data read for these three lines. In addition, with respect to the partial reading part, preferably, data on the head line of the partially read part is read twice and data on a line below the head line is read once when reading data on the head line of the partial reading part, and data on the last line is read twice and data on a line above the last line is read once in reading data for the last line of the partial reading part.
Further, preferably, the out-part data read for use in modification of the in-part data is changed into background data. With this arrangement, the out-part data contains no character data, so that bordering processing based on out-part character data can be prevented.
In such a case, when reading character font data, data on lines above and below a data reading line is read together with data on the data reading line so that data on the data reading line is modified based on the data read for these three lines. In addition, with respect to the partial reading part, data on a line above the head line is fixed as background data in reading data on the head line of the partial reading part, and data on a line below the last line is fixed as background data in reading data on the last line of the partial reading part.
Still further, a preferable modification of the in-part data is bordering of a character.